1. Field of the Invention
This invention relates to a method and apparatus for formation of reinforced concrete slabs (floors) in a multi-storied building, and, in particular, to the movement of the slab form panels from story-to-story.
2. Description of the Prior Art
When erecting multi-story, poured-in-place concrete structures, it is advantageous to make up slab form panels large enough to form an entire bay or large enough to approach the safe lifting capacity of the job crane. In addition to providing consistent quality of the slab surface, the goals of any system designed to accomplish this include:
reduced time on slab forming; PA1 reduced labor costs on slab forming; PA1 reduced costs of the equipment; PA1 increased safety for the workmen; PA1 increased safety for the structure; PA1 reduced weight of the equipment;
The most important feature of any such system is quality and efficiency of movement of the form panels from floor-to-floor.
Dave, U.S. Pat. No. 2,966,718 describes a system of form panels which are moved about on an adjustable carrier and transferred from floor-to-floor up a temporary ramp through a temporary hole left in the slab. The panels are restricted in size as they all must be maneuvered around columns and walls to the base of the ramp. As a result more joints between panels increase the labor in dealing with them. Also, considerable labor is involved in dismantling, moving, and erecting the ramp, forming the slab edges around the temporary opening, and forming the remainder of the slab to fill in the opening after the panels have been raised. The additional cost of overcoming the discontinuity of the reinforcing steel and concrete at the opening must also be considered.
Quentin, U.S. Pat. No. 3,482,005 involves temporary loading platforms which extend outside the building edge. Rolling form panels are maneuvered onto these platforms to enable attachment of the crane cable to the center of gravity of the form panel for lifting to the next floor. The length of the panel is restricted by the length of the platform extension and the cost and weight of the platform increases exponentially as one attempts to use a longer panel. Whether the panels are moved with a few platforms set several times, or several platforms set a few times, the additional time, labor and materials is still costly and dangerous.
Colnot, U.S. Pat. No. 3,450,280 mentions in his description of the prior art a `C` shaped or fork style hoist line implement which can reach around underneath the poured-and-cured floor slab edge and attach to the center of gravity of the form panel. By locating the crane cable vertically in line with the same center of gravity it maintains the panel in horizontal attitude when it is lifted inches clear of the floor on which it rests, to allow for lateral movement by the crane out from under the slab it had just previously formed. Colnot goes a step further by devising a boom-like hoist line implement which attaches to the projected end of a form panel and extends over the last poured slab above to an intersection with a vertical line through the center of gravity of the panel. The crane cable is attached at this intersection, a slight vertical lift clears the panel from the floor on which it rests, and the crane moves the panel out from under the floor last formed. Such a device develops higher tension and compression loads at the boom-panel connections than the total weight of the panel itself. It requires a skillful crane operator to move more than half the length of the panel laterally without jamming it between the columns on the side of the bay, or between the floor and ceiling. The panel must also be strong enough to resist bending for more than half its length. Such a need has led to the use of a parallel chord truss as the primary longitudinal beam in the form panel configuration, which is costly and heavy. Again, it is noted as the length of the panel (and so the boom) increase, the weight and cost of both increase exponentially.
It was soon discovered that this form panel now composed of parallel chord trusses, designed to resist bending in more than half its length, could be extracted from under the slab without Colnot's boom at all. Floor mounted rollers contacting the bottom chord of the truss enable the panel to be pushed out from under the slab. When the center of gravity of the panel has cleared the last roller at the edge of the slab the outer end of the panel begins to tip down until the top of the tail end jams against the ceiling. Since the center of gravity has cleared the edge of the slab above, the crane cable can now be attached directly to the panel at the center of gravity. As the crane lifts upward the panel returns from the tipped-down to a horizontal attitude and then begins to clear the floor on which it rested. Once clear of the floor the crane moves the remaining half of the panel laterally until it has cleared and slab edge and can be lifted vertically to the next floor. At the point of tip-down, when the center of gravity of the panel has passed the last roller at the edge of the slab, the entire weight of the panel is concentrated on that delicate point of the structure. As the panel continues out past tip-down a leverage effect increases that load in addition to an uplift load at the tail end of the panel. There is also a loose collection of jacks, rollers and dollies which require time and labor to move from panel to panel as the panel extraction progresses.
Avery, U.S. Pat. No. 3,899,152 proposes the use of specialized extruded aluminum `I` beams as the material from which to fabricate the truss in an attempt to reduce the weight. Not only is the panel still heavy, but lacks in resiliency compared to steel, and is expensive due to the aluminum and the specialized shape.
Daskew, U.S. Pat. No. 3,966,164 and Moore, U.S. Pat. No. 3,977,536 attempt to make the truss system more workable by increasing the ease of adjustment and maneuverability. The basic problems with the system still exist and these improvement ideas decrease labor but increase material cost.
Strickland, U.S. Pat. No. 3,504,879 describes an adjustable jack with a top roller which is bolted near the top of previously poured concrete columns on each side of a bay as supports for a form panel. Instead of the truss mentioned above as a primary girder in the panel, he uses a very deep wide flange steel beam with the same resistance to bending as the truss. The panel is pulled out of the building on the rollers and tips down when the center of gravity of the panel has passed the last column-jack-roller. The same concentrated loads have to be delt with but this time on less-than-fully-cured-columns, instead of the slab edge. Since the primary beams in the panel have to be at the outer edge of the panel, the joists or secondary beams in the panel have to span further and, therefore, be stronger and heavier than a joist supported at approximately one quarter and third quarter points. Such a panel is heavier than an aluminum truss panel of comparable size and has very limited adjustment for width. It requires sleeving of the column as well as mounting and dismounting of the cumbersome roller jacks. As a result of the inherent problems, such a system has relatively specialized usage.